Qs about What machine work is critical…

[DarkHelmet]

Given the masters of the dark arts are all...restricting their work..., I'm left with sourcing various shop labor from multiple vendors who specialize on only one thing here or one thing there. I have questions on what exactly is critical in engine work and what is just fine as it came from the factory.

I'm getting two small bore heads worked on, both 12g202. one a wonderfully ported head from the 80s for an SCCA midget that needs exhaust seats installed (available easily) and the other head is so pitted it needs both seats and valves all around. The intake seats are not found anywhere for the 12g202 size intakes, however I see the 1275 exhaust valves are the exact same size of my 12g202 intake valves.....so....can those available seats be used on my intake side of the 12g202 head? ( i would assume so since same size valves...here's no way around it) or are seat inserts available from any machine shop because they have boxes of all sizes like o-rings..? I dont know.

I'm finding places to bore a 1275 block I have. It's already .040 over but it's been used in that state a while and the bores are a bit ovalised and i think on the outside edge of too large for re-honing and re-ringing what i have. I'm learning as long as the bore spacing between 2 and 3 is .120 or more i can safely go to .060, without offset boring. I don't think i can start offset boring if it's already at .040, but if that's the case, and i have the room, i can go 60 over...but that leads to the next question.

Rods. I have the big square bottom heavy rods. They're good. But heavy, so what. However they have press fit pistons and they have the 40 over AE pistons already on there...and if I'm going 60 over, i need to remove the pistons...well, how? Just heat everything up? I see lots of vids on installing omega pistons, but nothing on removing them. (I have a set of same rods with 30 over AE's on there if anyone's interested)

And more rod questions. In the chase for making sure everything is round, assuming the crank is prepped and the bearings are properly sized, should I only need to slap bearings in and bolt it all up? Or is there a process of making sure once torqued up the rod big ends are actually round....as I see total race shop guys doing, is that important here or something that's fine to go as is as it came from the factory as long as my plastigauge checks out? (BMC made all of this with fine precisions hammers...so we can trust it right?)

Typing from a hotel room...not near the yellow bible.

Coming up, the hardened seats going into the mystery midget1100 race head i sourced will go on the mystery 1098 in Winston right now that i think has a metro cam (ill know for sure when the head comes off and i can look into the tapped chests). Should breather better now it wont have crazy pitted valves and carbon build up.

[MiniDave]

My local head shop provides hardened seats for any of the heads I take to them, no problema.....since they're the ones installing them I think they actually prefer to supply them too. They then cut the seats to match the valves I give them.

The machine shop that will bore the block should be able to check your rods and hone them round if needed....my shop also checks to make sure they're straight, and can adjust them as needed too.

Again, if you're using a shop to bore the block, they can press the pins out of the old pistons and press them in the new ones too. My shop heats the pin end of the rod, then the pins slip right in - it's important to get them in just enough so that they're centered. They'll want the new pistons anyway to bore the block to....they can offset bore if needed. I had one block that had a gouge in one side from a pin that got loose - they were able to offset it only 4 thou to clean up the bore.

I have a difficult time finding a shop to bore a 998 or 1098 block as the bore is smaller than their machine will go, 1275's are just big enough that they can do them ok.

You need to mic that crank and make sure the journals aren't worn out of round or tapered. Again, the machine shop that can turn a crank can do that for you - and will to make sure of what they're doing. If it's a competent shop they'll machine the crank to the proper size, then yes - just use plasti gauge to double check the clearances and you're good to go.

[DarkHelmet]

Thanks Dave.

I finally got to measuring the 1310 used block I have. It mic'd out at basicly 2.8221 to 2.227" front /back and left/right each cylinder top and bottom areas of travel. This after the drill stone+wd40 hone I did a while ago when I got it last summer. I cant feel with fingernail or finger the top ring but its like a semi-visible shadow. Anyway, given the piston measurement of 2.8184 (ae21253 +.040 9.75:1 cr)and doing math, the cylinders are 0.004"+ over the piston measure which I believe falls withint he maximum piston to wall clearance. The cylinders all measure very close and appear by those numbers they are decently round and only vary by .0005 at most and not really at all tapered, some reflecting same numbers top to bottom. It's just they might be at the maximum bore for this .040 piston. In theory I could make sure I have a nice cylinder wall pattern and ring them up and put them in after I get the crank ground to the new undersize, but it would be at the limit of doing that I guess.

Or, get 60's and bore it. knowing I would be at about .135" between middle cylinders and safe.